The proposed work will develop a theoretical basis for interpreting experiments of time resolved elastic light scattering. The hemoglobin of sickle red blood cells, unlike that of normal cells, binds to other hemoglobin to form long straight fibers, which when aligned in domains cause the blood cells to become rigid. Light scattering, through the use of microsecond photolytic pulses, has proven to be a useful probe for studying the kinetics of this polymerization process. Previous theories of light scattering have been developed only for dilute concentrations of polymers, yet concentrations in red blood cells are dense. In order that analyis of the entire polymerization process and formation of domains might be possible, light scattering theory will be developed in order to include conditions ranging from dilute to concentrated. The proposed research is composed of two parts. The first part involves a continuation of the study of the early part of the polymerization reaction, for which the concentration of fibers is dilute and multiple scattering effects may be neglected. Models will be developed for the distributions of sizes, spatial positions and orientations of polymers, and these will be used to calculate the angular distribution of polarized scattered light as a function of time and of wavelength of the incident light. The second stage of research involves a study of the later part of the reaction and the formation of domains, when the concentration of fibers is dense and interference and multiple scattering effects are important. We will use an effective medium approach, coupled with the inclusion of multiple scattering to calculate the consequences of these effects on both the angular distribution and magnitude of light scattering as a function of wavelength and on the birefringence. This theory will be applicable not only to sickle hemoglobin but to high concentrations of spherical or cylindrical scatterers in other biological systems and will enable light scattering to test a wider range of kinetic theories.